In Japan, soaking in natural hot springs is a treasured pastime that’s steeped in thousands of years of tradition, and during my stay there, I visited a few. The experience opened my eyes (and pores) to a world of good-feeling benefits, many of which (but not all) are backed by a plethora of research.

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Confession: Before my recent visit to Japan, I never bathed. That’s because I shower. My Japanese friends, on the other hand, grew up viewing their daily bathtime and hot springs (generally referred to as onsen in Japanese) as mandatory, a time to relax and reflect. The rest of us also sort of instinctively feel that baths—and by extension, hot springs—can be good for the mind and body, but to what extent?

First, Hot Springs as Medicine Is Still An Area of Research

To the Japanese, hot springs are more than just a “hot tub”—they’re precious for relaxation, health, and more. Of course, it’s not just the Japanese. Hot springs, onsens, mineral baths, spa therapy—whatever you want to call them—have a rich history and are cherished in many parts of the world.

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That’s because hot springs are reputed to have a number of therapeutic benefits. According to folklore, soaking in hot springs increases your blood flow, circulation, metabolism, and absorption of essential minerals. Sounds awesome so far, but wait—there’s more! A poster at the popular hot springs I visited in Noboribetsu, Hokkaido that I had a friend translate said that their waters could help “treat chronic digestive diseases, constipation, diabetes, gout, and liver complaints.”

Okay, this all may sound like voodoo magic, but many scientists from Japan, Europe, the Middle East, and elsewhere have long been studying balneology (or balneotherapy), which is the “treatment of disease by bathing” and usually in waters containing minerals. This field of medicine is not very well known nor understood yet, but continues to be an exciting area of research for people who’d like more reason to cozy up in some hot springs. Balneology, especially in Japan and Europe, has been used as natural medicine and preventative therapy for centuries.

Meanwhile, you probably won’t hear “splash around in hot springs” as part of a prescribed treatment by your doctor, as a grip of studies on the subject seems to echo this particular quote by the authors of this paper in The Journal of Epidemiology: “The effectiveness of balneotherapy in curing disease or improving health remains unclear.”

But that hasn’t stopped people from enjoying their thermal baths and hot springs for thousands of years.

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What Do the Minerals in the Water Do?

Since many hot springs contain sulfur, prepare to get repeatedly good whiffs of hydrogen sulfide, the jerk responsible for that rotten egg smell (don’t worry, you kind of learn to love it). There can be many other minerals in the waters, too. Typically, you’ll find calcium, sulfate, magnesium, iron, chloride, potassium, zinc—to name a few.

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When dissolved in heated water, these minerals are thought to confer specific—but mostly unproven—health benefits. Currently, it’s not really known how or if you get more of these minerals into your body by simply bathing in them. There are many factors that can influence absorption through the skin. Under normal circumstances, our outermost layer of skin, mostly made up of dead skin, is really dang good at keeping things out, especially in water. Otherwise, we would be in hot water (excuse the pun) any time we swam around in the ocean.

Some suggest that sweating, the opening of pores, and hydrated skin from hot springs can increase absorption, and it’s possible something could happen, at least on the surface of the skin. Certainly, there are accounts of people who’ve experienced some relief from their skin-related conditions, like less flakiness and redness. An early German study suggests that it may be the the effect of magnesium; still others, looking specifically at waters from the Dead Sea, chalk it up to its uniquely high salt content and mineral profile.

One particular Japanese hot spring I went to seemed to have already figured these things out, as each of the seven different pools had different mineral concentrations and make-ups for different health-related purposes. The oh-so-many choices included a sodium-calcium-chloride pool for making the skin feel youthful; a calcium-magnesium pool to help with allergies and inflammation; a sulphur- and iron-containing pool that they proclaimed to be “a universal cure-all,” and more. (You were even encouraged to drink their hot springs water from a special fountain though you shouldn’t generally do this, lest you’re okay with gulping down harmful critters).

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The type of hot spring didn’t matter to me though, since I couldn’t read the Japanese signs anyway. I simply went wherever curiosity took me and stayed when my body gleefully screamed “Heck, yes!” And I believe that’s the whole point.

The “Magic” is Probably in the Water Itself

Whatever the case, hot springs still feel heavenly. A large part of the virtues of hot springs are owed to the properties of water itself, along with the heat.

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As you so cleverly deduced, hot springs are generally pretty hot, typically measuring around 37-degrees Celsius (or 100-degrees Fahrenheit) or hotter. Each of the pools I dipped into also ranged from 37-degrees Celsius to 42-degrees Celsius, with the idea being that people would go to each pool and gradually ease their bodies into hotter and hotter temperature baths.

This heat, although sometimes intense, can help relieve pain. The way it works, as this meta-analysis of studies published in the North American Journal of American Sciences suggests, is that the heat along with the pressure of the water dulls our perception of pain by blocking the pain receptors in our bodies. Plus, the mineral concentration and hot water can make you feel “floatier”, which has positive effects on your joints and muscles, working together to help you feel good and—more importantly—more relaxed.

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Most of us have confirmed this, at least empirically: Our achy joints and cranky muscles from a rough workout or just life in general tend to feel alive again after a hot soak. A review in Rheumatology revealed that spa therapy and balneotherapy may be able to help relieve lower back pain, specifically at higher temperatures. If you really want to make the most out of your soak, Paul Ingraham over at PainScience.com suggests combining a little self-massage and gentle stretching to feel awesome.

One crucial precaution to bring up, however, is that immersing yourself in hot water can up your body temperature and loss of water through sweat (though you wouldn’t easily notice it when you’re already wet). After a while, you might feel lightheaded and/or dehydrated so be sure to drink plenty of extra water during and after (since we don’t always remember to do so beforehand). I found my limit to be about 15 minutes of continuous soaking before the baths got to be too much for me.

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Go For the Possible Benefits, Stay For the Stress Relief

The thermal benefits go beyond helping to relieve pain and aches. Researchers from Japan found that soaking subjects who had chronic heart failure in hot springs actually led to a decrease in blood pressure and improved their symptoms. It’s a pretty radical (and small) study, but there are other instances where the thermal and mechanical properties of hot springs can help the body.

As you sit in hot springs, your blood pressure drops, your circulation goes up, and your metabolism kicks up a bit. You’ll probably feel a little funny, too, at first, but eventually, you adjust to the temperature and all is right in the world.

What’s more: because you can actually relax, you lower your anxiety and stress and can create rippling physiological benefits throughout. We all know that stress—the type that keeps you awake at night and messes with your quality of life—is bad news for our long-term livelihood; and the researchers responsible for this study in Advances in Preventive Medicine propose that hot springs are effective at reducing stress and improving things like sleep quality and appetite.

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Most of us probably don’t need much convincing to get into the habit of hot springs, if they’re convenient, but it’s good to know that hot springs are amazing for stress relief.

Hot Springs As Part of a Healthy Lifestyle

We don’t get super strong or fit from just a single workout, nor do we suddenly reverse years of eating crap by eating a single piece of fruit. So it’s probably safe to say the real benefits of hot springs come from habitual use, as part of a holistic approach to health.

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People enjoy their hot springs for various reasons, beyond health and stress relief. During my time in Japan, I learned that baths and hot springs are treated as everyday, sometimes communal activities, especially if you head to hot springs or public bath houses. It’s normal (and inevitable) for strangers to see one another naked, but it’s even more normal for them to use these public spaces as gathering places for families, friends, and communities to enjoy a good soak together.

For most of us though, visiting hot springs regularly probably isn’t convenient or realistic, but any time you can unwind and get away from stress—perhaps some alone time with Mr. Rubber Ducky in a hot bubble bath—can do wonders for your body and mind.

That was, after all, what I’d been hoping for myself on my visits to hot springs. I didn’t know about all the (specific) purported benefits at the time nor did I expect to have my own eczema conditions fully healed. I just knew that I wanted to relax and get to experience first-hand what I saw in those pictures of snow monkeys blissfully chilling in hot springs.

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And that’s exactly what I did.

Illustration by Sam Woolley.

Stephanie Lee is a nomadic writer with a Sriracha problem. Visit her blog at http://fitngeeky.tv/ for her lighter takes on fitness and her shenanigans. You can also follow her on Twitter and Facebook.